Acoustic reflex ear protective system



Sept 69 1966 J. L. mama-2ER HAL L@ ACOUSTIC REFLEX EAR PROTECTVE SYSTEMJ5 Sheets-Sheet l Filed Dec. 4, 1962 \N\/ENTO25 JOHN L.. FLETCHER AQTH Q.QwPELLE.

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ATTcaNE/ Sept- 5, 1966 @L L. FLETCHER mmm 39271952@ ACOUSTIC REFLEX EARPROTECTIVE SYSTEM Filed Dec. 4, 1962 5 Sheets-Sheet B /e l N/ *.l

5/ a/ Il os@ LLA-V02 3/) AAA vv BY (mab/Mb ATTO @may United StatesPatent O 3,271 520 ACOUSTIC REFLEX EAR? PROTECTIVE SYSTEM John L.Fletcher, Fayettevilie, Arlt., and Arthur J. Riopelle, Orange Parli,Fla., assignors to the United States of America as represented by theSecretary of the Army Filed Dee. 4, 1962, Ser. No. 242,337 1 Clmm. (Cl.179-1) The invention described herein may be manufactured and used by orfor the Government for governmental purposes without the payment to usof any royalty thereon.

This application is a continuation-in-part to application Serial No.67,443, filed November 4, 1960, now Patent No. 3,068,319.

The present invention relates to an acoustic reflex ear protectivesystem and more particularly to an acoustic reflex ear protective systemfor introduction of a sound to the ear anticipatory to the reception ofa second sound to the ear such that the ear is protected fromnoise-induced hearing ioss.

The introduction of a sound at the level of 80 to 110 decibels, forexample, into the human ear causes a brief contracture of the stapediusand tensor tympani muscles of the middle ear and tightens the eardrum.The tightened eardrum is less free to vibrate and thus less able totransmit sound vibrations to the fluids of the inner ear. Thiscontracture is termed the acoustic reflex.

A system exemplary of the present invention may include a source ofenergy, a pair of energy paths connected in parallel to the source,sonic generator means connected to each path and actuated by the energysource, and energy impeding means positioned in one path between thesonic generator means and the energy source such that actuation of onesonic generator means precedes actuation of the other sonic generatormeans by the energy source whereupon the sound produced by thefirst-actuated sonic generator means conditions by acoustic reflex theear for reception of the sound produced by the lastactuated sonicgenerator means.

A second example of this invention comprises the programmed introductionof continuous protective sound or continual protective sound stimuli insituations where there is no control over the distressing sound.

An object of the present invention is to provide a new and improvedacoustic reflex ear protective system.

Another object is the provision of an ear protective system to induce asound to the ear to actuate acoustic reflex in advance of the receptionof sound which otherwise could cause noise-induced hearing loss.

Still another object of this invention is to provide a system includingcircuitry adapted for use with standard military equipment.

A further object of part of this invention is the provision of an earprotective system which causes delay of the production of a deafeningnoise until after the production of a sound capable of conditioning byacoustic refiex the ear for reception of the deafening noise.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawing in which like referencenumerals designate like parts throughout the figures thereof andwherein:

FIG. 1 is a block diagram of the general concept of one embodiment ofthe invention;

FIG. 2 illustrates in schematic circuitry a portion of the embodiment ofFIG. 1 disconnected from an input section of an audio frequencyamplifier;

FIG. 3 is a view of the specific circuitry of the input section of anaudio frequency amplifier of the embodiment 3,271,520 Patented Sept.` 6,1966 lCC of FIG. 1, connected with the output of an oscillator sectionof the system;

FIG. 4 is a block diagram of a further embodiment of the invention forproducing a programmed, continuous noise; and

FIG. 5 is a block diagram showing a modification of the embodiment ofFIG. 4 including means for modulating the'programmed, continuous noise.

The first embodiment, illustrated in FIGS. l3 is i1- lustrative of anear protective system wherein. control of the distressing sound ismaintained.

Referring to FIG. 1 there is shown a voltage supply 11 connected to afiring trigger or switch 12 which is in series with a delay section 13of the protective system. The output of the delay section 13 is fed to atiring solenoid 14, which, when energized upon closing of the switch 12,actuates by mechanical linkage not shown, the firing mechanism of a gun15, for example.

An oscillator section 20 illustrated in FIG. 1 is connected in parallelwith the delay section 13 to the switch 12, as best shown in FIG. 3,with an output terminal 17 connected to the input point 18 of an audiofrequency amplifier and mixer 19, FIG. l. The amplifier and mixer 19 isidentified as AM-65/ GRC by the U.S. Army, and is described in detail inTechnical Manual 1l-5039, an Army Signal Corps publication availablefrom the U.S. Army Publications Branch, Office of The Adjutant General,the Pentagon, Washington 25, D.C.

Basically, the audio frequency amplifier and electronic mixer 19includes three `channels 21 and is designed to provide interphoneoperation `and radio monitoring in installations using one or tworeceiver-transmitters and one or more interphone control boxes. Theinstallation shown in FIG. l includes, for example, a radioreceivertransmitter 22, designated by the U.S. Army as RT- 70/GRC, whichis used for radio and interphone operation. The radioreceiver-transmitter output is fed to input 23 of the amplifier andmixer 19. Input 24 of the amplifier and mixer 19 is used for a radioreceiver and interphone, generally designated as numeral 25. Input 26 isavailable for intercommunication only between local stations, and has aparallel connection which serves as the input point 18 from theoscillator section 16. Control boxes 27 are selectively connected bythree-position switches 28 to output channels 21 of the amplifier andmixer 19 and are in turn serially connected to headsets 31. The controlboxes 27 are identified as C-375/VRC by the U.S. Army in TM 11-5039,referred to hereinabove.

As shown best in FIG. 2, the oscillator section 16 of the ear protective`system includes the output terminal 17 connected to an output volumecontrol 29 of an oscillator 31, FIG. 3. A relay 32 with pairs ofcontacts 33 and 34 has its actuating coil 35 operatively connected tothe voltage supply 11 at terminals 36 by the trigger or switch 12. Therelay 32 is actuated to close contacts 33 to complete a circuit from theoscillator 31 to an input section 37 of the audio frequency amplifier19. Also, actuation of the relay 32 closes the contacts 34 to complete acircuit from the supply 11 to ground through a relay 38 which in turncloses contacts 39 to complete the connection between the oscillator 31and the `audio amplifier 19.

The oscillator 31, FIG. 3, is a conventional R.C. coupled transistoroscillator, and, in the preferred embodiment of the invention, isdesigned with an output of approximately one volt at 1000 cycles persecond. The oscillator 31 is powered by a 22.5 volt battery 41, for eX-ample, with the oscillator output appearing at terminal 17, which isconnected through the output volume control 29 to the input point 1S ofthe amplifier 19.

A circuit for energizing the solenoid 14 is shown in FIG, 3 to includerelays 42 and 43 in series arrangement having pairs of contacts 44 and45 with coils 46 and 47, respectively. The relays 42 and 43 connect thesolenoid 14 with the switch 12 and the voltage .supply 11, and are inparallel with the relay 32. A charging capacitor 48 and a variableresistor 49 are provided for delaying the actuation of the solenoid 14by the source 11.

Cannon sockets 51 are utilized in the schematic views of the system inFIGS. 2 and 3 as terminal blocks.

The operation of the first embodiment is initiated by the firing trigger12, which may be a hand gripped electrical switch, is closed by anoperator whereupon 24 volts, for example, are applied from the voltagesupply 11 to the charging capacitor 48 and the variable resistor 49. Thecurrent sensitive relay 42 has its coil 46 energized upon charging ofthe 100 microfarads, capacitor 48 for example, at which time thecontacts 44 of the relay 42 complete the circuit for energizing therelay 43. Through the closing of the contacts 45 of the relay 43, the24-volt circuit is completed to the solenoid 14, causing a gun 15, forexample, to fire.

Also, when the firing trigger 12 is closed, 24 volts from the supply 11are applied to the relay 32, energizing the coil 35 and causing the twoysets of contacts 33 and 34 to close. The closing of contacts 34energizes the relay 38 in the input section 16 of the amplifier 19 tocomplete an input circuit, and the closing of contacts 33 completes thecircuit from the output terminal 17 of the oscillator 31 to the inputpoint 18 of the amplifier 19. The output of the amplifier 19 isdistributed to one or more of the control boxes 27 and is then fed intoearphones 31 worn by an operator to cause an acoustic refiex in hisears. The delay in the firing circuit caused by the charging capacitor48 is sufficient to permit reception of the output signal from theamplifier 19 into the ear of an operator through headsets 31 prior tothe energization of the solenoid 14 which causes a gun 15 to fire, forexample. Accordingly, the ears of the operator are protected from thedamaging effect of the gun noise by activation of the acoustic reflex bythe output of amplifier 19 in advance of the firing of the gun.

The second embodiment of which FIGS. 4 and 5 are species provides forprotection against continuous distressing noise or continuous protectionagainst noncontinuous distressing noise over which control is notmaintained.

In the species of FIG. 4, the acoustic reflex is activated andmaintained in its activation by cycle per second pulses or clicks Thesepulses are generated by a multivibrator and amplified by an audioamplifier with a good low frequency response and fed into earphones orspeakers. Research has shown that pulses at 15 c.p.s. at a proper soundpressure level at the ear of about 105 db re .0002 dyne/cm.2 willactivate the reflex `and keep it contracted. Although the reflex sounddecreases hearing due to exposure to background noise, the hearing isnot otherwise affected by the sound. In the species of FIG. 5, a ringmodulator acting in combination with a signal generator and the 15c.p.s. pulses from the multivibrator enable an audio amplifier ofinadequate low frequency response to be used in the system. If the audioamplifier can faithfully reproduce the 15 c.p.s. pulses, the ringmodulator and the signal generator may, of course, be eliminated. Inthis system, unlike the first embodiment (FIGS. 1-3) the sound producer(multivibrator) is turned on manually before exposure to the noise forwhich protection is desired, left on as long as the noise persists, andturned off manually when the noise exposure is terminated. It does notinclude control of the source of the hazardous noise.

The above-mentioned components are well known to those skilled in theart and are commercially available. No Ispecification or limitationsother than mentioned above are required.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. For example, the relay43 may be omitted if the contacts 44 of the relay 42 are capable ofcarrying the 6 ampere current, in the preferred embodiment, necessary tooperate the firing solenoid 14. Similarly, the audio amplifier 19 may beomitted from the ear protective system should the output power of theoscillator 31 be sufficient to deliver the acoustic energy required tocreate acoustic refiex in the human ear. It is therefore to beunderstood, that within the scope of the teachings herein, the inventionmay be practiced otherwise than as specifically described.

We claim:

Apparatus for producing continuous sound for placing the ear in acousticreflex condition for continuous protection against distressing noisecomprising:

(a) a multivibrator continuously producing pulses at the rate of l5cycles per second;

(b) a signal generator;

(c) a ring modulator electrically connected to said signal generator andsaid multivibrator;

(d) an audio amplifier electrically connected to said ring modulator;and

(e) a speaker electrically connected to said audio amplifier, saidspeaker impressing the continuous 15 cycle per second pulses upon theear thereby producing the acoustic reflex condition.

References Cited by the Examiner UNITED STATES PATENTS 10/1956 Konrad340-384 12/1962 Fletcher et al. l79--l.8

